With the technologies of semiconductor process and IC design continuously progressing, ICs with different functions are widely utilized in various products. Meanwhile, the critical dimension of semiconductor components is advanced to a scope of sub-microns, and even to that of deep sub-microns, so that the integrity of IC is increased rapidly. Since there is no sufficient area on the surface of semiconductor structure for producing the interconnections required by semiconductor components, the technique of multilevel interconnection is developed to perform the interconnection and insulation among semiconductor components by utilizing several metal layers and dielectric layers, and the metal interconnections used for supplying power to semiconductor components construct the power network of IC.
In an IC within the deep sub-micro scope, the process and transmission of signal are always interfered by noise greatly, such as leakage current noise, crosstalk noise, reflection noise and power supply noise, etc., wherein the higher the operation frequency of IC is, the more serious interference of the power supply noise will be, so that the analysis of power network is needed.
In analyzing the performance and efficiency of a power network, the electromigration and voltage drop are two major factors that need to be stressed. If the current density driven through a piece of conductive metal line is too high, then the atoms in the metal line will be migrated along the conductive metal line. This phenomenon, known as electromigration, will eventually result in the deterioration of the conductive metal line and the failure of the semiconductor circuit.
In order to let semiconductor components located on different locations receive sufficient operation voltage, excessive voltage drop in a chip has to be avoided. In other words, if the voltage drop occurring in the operation of some on-chip semiconductor components is too large, then the voltage received by the other on-chip semiconductor components (especially by the semiconductor components located on the center portion of the chip) will not be sufficient for operation. Therefore, the performance and efficiency of IC is decreased, and even the erroneous operations will be caused.
With the substantially increasing operation frequency of IC, the switching speed of on-chip semiconductor components is increased synchronously. Since voltage pulses are caused by electrical variations in the switching state of semiconductor components, these voltage pulses will cause temporary voltage drop to the operation power average, and will cause noise between power supply and ground. Therefore, the noise is increased substantially with the increase of operation frequency, transmission speed and density of IC, thus affecting the regular operation of system and causing wrong behaviors.